1. Technical Field
The invention relates to a manufacturing method of a solid-state imaging device configured so that one photoelectric conversion layer is laminated above a semiconductor substrate.
2. Description of the Related Art
In a single-plate-type color solid-state imaging device as represented by CCD-type or CMOS-type image sensors, three kinds or four kinds of color filters are arranged in a mosaic shape on an array of light-receiving sections, which perform photoelectric conversion. Accordingly, color signals corresponding to the color filters are output from the light-receiving sections, respectively, and these color signals are processed to generate a color image.
However, the color solid-state imaging device in which the color filters are arranged in a mosaic shape is not good in light use efficiency and has low sensitivity because about ⅔ of incident light will be absorbed by the color filters when they are color filters for primary colors. Further, since only one color signal is acquired by each light-receiving section, resolution is not good, and particularly, false color may become conspicuous.
Therefore, in order to overcome the problems, an imaging device having such a structure that three photoelectric conversion layers are laminated on a semiconductor substrate formed with a signal read circuit has been studied and developed (for example, see JP 2002-502120 T (corresponding to WO99/39372 A2) and JP 2002-83946 A). This imaging device has, for example, such a structure of a light-receiving section that photoelectric conversion layers, which generate signal charges (electrons, holes) with respect to red (R), blue (B), and green (G) light components, are overlapped on each other sequentially from a light incidence plane and that each photoelectric conversion layer is provided with a signal read circuit, which can independently read a signal charge generated in each photoelectric conversion layer.
In the imaging device having such a structure, most of incident light is photo-electrically converted and is read and thus, the use efficiency of visible light is close to 100%. Also, color signals for three colors of R, G, and B are acquired by the light-receiving sections, respectively. Therefore, a good image with high sensitivity and with high resolution can be created (false color is not conspicuous).
In order to actually achieve imaging devices as described in JP 2002-502120 T and JP 2002-83946 A, a photoelectric conversion section formed above a semiconductor substrate is configured as follows, for example. That is, a large number of photoelectric conversion sections are arranged on the same plane above the semiconductor substrate. Each of the photoelectric conversion sections includes a first electrode laminated above the semiconductor substrate, a photoelectric conversion layer formed on the first electrode, and a second electrode formed on the photoelectric conversion layer. The first electrode is partitioned for each of the large number of photoelectric conversion sections. The photoelectric conversion layer and the second electrode are common to the large number of photoelectric conversion sections.
In such a solid-state imaging device having the large number of photoelectric conversion sections, it is necessary to provide an electrode pad for connecting a power source to the solid-state imaging device as in a single plate-type solid-state imaging device. In the single plate-type solid-state imaging device, after the electrode pad is formed on the semiconductor substrate, an opening is formed in the electrode pad by photolithography technique to expose the electrode pad whenever a laminate (e.g., a color filter and a micro lens) is formed on the semiconductor substrate.
Even in the above solid-state imaging device having the large number of photoelectric conversion sections, it is necessary to expose the electrode pad. However, the photoelectric conversion layer made of an organic material is weak against heat or moisture as with the single plate-type solid-state imaging device. Thus, when a process of forming an opening in the electrode pad by the photolithography technique is employed whenever a laminate (e.g., the first electrode, the photoelectric conversion layer and the second electrode) is formed on the semiconductor substrate, the performance of the photoelectric conversion layer may be degraded. Further, in the solid-state imaging device having the large number of photoelectric conversion sections, when the second electrode is formed, it is necessary to form wiring lines for connecting the second electrode to the electrode pads. Since the second electrode itself is configured as one sheet common to each photoelectric conversion section, the photolithography technique is unnecessary, but it may become necessary to pattern wiring lines for connecting the second electrode to the electrode pads by the photolithography technique. As described above, in the solid-state imaging device having the large number of photoelectric conversion sections, after the photoelectric conversion layer is formed, it is important to expose the electrode pads and to form the wiring lines between the second electrode and the electrode pads without using the photolithography technique becomes in order to prevent degradation of the performance of the photoelectric conversion layer.